1) Field of the Invention
The present invention relates to an apparatus for separating liquid from a gas/liquid mixture, comprising: a housing; a gas/liquid mixture inlet located at a lower side of the housing; a coalescer placed in the housing above the gas/liquid mixture inlet for extending the volume of liquid droplets from the mixture passing the coalescer; at least one liquid feed, which liquid feed runs at least partially through the coalescer and ends at location below the gas/liquid mixture inlet; a liquid outlet for the separated liquid fraction located at a lower side of the housing under the coalescer; and a gas outlet for the separated gas fraction located at an upper side of the housing above the coalescer.
2) Description of Related Art
Such coalescers are used in the technology field of extraction of hydrocarbons (oil and gas). The extracted product usually consists liquid (oil and water) and gas to be primary separated in e.g. cyclone separators. The resulting mainly gas phase fraction from such primary separation normally still contains a substantial amount of smaller liquid droplets to be further separated in a coalescer. Such a coalescer is also known as a “demister” and makes use of a porous material or vanes placed in a vertical or horizontal tube (vessel) where through in upward direction the gas/liquid mixture is fed. During passage of the coalescer a part of the (relatively small) liquid particles (droplets) in the gas/liquid mixture will collide with the coalescer material resulting in growth of the average particle size. Dependent on the upward speed of the supplied gas/liquid mixture due top gravity the larger droplets will drop to the underside of the housing in—normally—a liquid bath. In this respect is also observed that already during the feed of the mixture in the housing (thus before passing the coalescer) larger liquid particles may directly drop down in the housing. The gas/liquid mixture inlet is normally located above the liquid bath in the housing. At higher upward speeds of the supplied gas/liquid mixture a part of the larger (and also smaller) droplets are carried along the coalescer resulting in a bubbling liquid layer on top of the coalescer from where liquid particles easily can be carried along with the gas phase fraction as droplets may be released again from the bubbling liquid layer. This will result in an over all lower separation. The bubbling liquid layer has as a further disadvantage that it prevents the proper functioning of the coalescer. An overloaded coalescer is “supersaturated”. The supersaturating of the coalescer is dependent on among others the velocity of the gas/liquid-mixture, the types of gas and the liquid. The skilled person is aware that supersaturation occurs when the K-value is ≧0.1. Also there apply high shear forces in the bubbling liquid layer. Finally the substantially separated fractions leave the housing via a liquid outlet that is located under the coalescer; and a gas outlet that is located at the upper side of the housing. The underside of the housing thereby normally acts as collecting means for the liquid leaving the liquid feed and falling downward from the coalescer and for the fluid fed back via the at least one liquid feed. The gas outlet is for discharging the gas fraction the dried (or at least drier) gas from the top of the housing, whereby the gas fraction still may contain liquid, however in a smaller proportion than the liquid fraction in the gas/liquid mixture originally fed to the housing.
To release the coalescer from the bubbling liquid layer coalescers are provided with one or more liquid feeds (also known as downcomers or through feeds) which runs through the coalescer to transport the liquid to a location below the coalescer, preferably the below the gas/liquid mixture inlet.
The known demisters have limited separation results and a limited capacity due to the limitation of the maximum upward speed of the gas/liquid mixture for proper functioning.